1. Field of the Invention
The present invention relates to a metal molding having metallically connected regions of metal foam, on the one hand, and metal, on the other hand, and of at least one insert element made of material having a higher melting point than the basic material of foam and metal, and also to a method for producing it.
2. Discussion of Background Information
Lightweight metal moldings and production methods of the type mentioned are known, for example, from AT 408317 B, according to which, in a powder-metallurgic method, a semifinished product body consisting of a compacted mixture of a matrix metal powder and of a propellant powder is heated in a foaming mold, together with at least one insert element, to a temperature at which the matrix metal powder melts and releases the propellant powder which forms gas bubbles in the matrix metal. The metal foam occurring envelopes the insert element which consists of material not melting at the temperatures used and which can fulfill the most diverse possible functions, such as, for example, the provision of connections, cavities, reinforcements and the like. Disadvantages of such metal moldings and of the production method are to be seen in the high outlay involved, along with the resulting costs, and, in particular, also in the division, controllable only with difficulty or even not at all, of the metal foam regions and metal regions, and in the broad distribution of the pore size in the metal foam itself, all this having adverse influences on the quality of the moldings.
In likewise known fusion-metallurgy methods for the production of metal foam itself (see, for example, AT 410103 B or AT 411970 B), gas is introduced into a metal melt reinforced with particles, the result of which the gas bubbles formed collect on the surface of the melt, thereby producing flowable metal foam. This metal foam then either is cast or pressed into a mold or can also rise directly into a mold arranged above the melt. The foaming gas in this case introduced into the melt by means of nozzles (see, for example AT 410104 B or AT 411768 B) or by means of what is known as an impeller (see, for example US 2003/0051850 A1). Metal foam is in this case produced predominantly from aluminum composite material, but additionally also from composites of magnesium or other light metals. The most comprehensive industrial experience has hitherto been based on aluminum foam which, from the point of view of the desired minimum mass density, is virtually ideal and also has outstanding properties in terms of energy absorption. Moldings consisting of metal foam are therefore used, for example, in the crumple zone of automobiles, as cavity reinforcements, but also as lost core parts of lightweight hollow castings reinforced thereby, said moldings additionally having a positive influence on solid-borne sound properties.
However, metal foam and moldings produced from it are capable to only a relatively small extent of absorbing tensile stresses, and attempts have already been made to improve this by means of the insert elements referred to initially. Further, there has also hitherto been an unsatisfactory outcome of attempts to provide any desired thickness or configuration of a solid, high-density and relatively foam-free outer wall region.